TEWKSBURY, Mass. — It was a highly unusual sight: business executives in suits alongside warehouse workers wearing tank tops, all rallying against changes in the management of their employer, a successful New England supermarket chain. But allied they were this week in an unusual labor action, fallout from the latest chapter in a decades-old family feud that pits two Arthurs against each other.

A broad cross section of employees of the chain, Market Basket, is seeking the reinstatement of their former boss, Arthur T. Demoulas, who was ousted last month as president by a board of directors led by his cousin Arthur S. Demoulas. The protest intensified Friday as more than 2,500 employees and supporters rallied here during the workday in the parking lot of Market Basket’s headquarters.

“Don’t have a doubt in your mind, the wolves are at your door, and they came for your boss,” Steve Paulenka, the M.C. of the rally, told his co-workers under a blazing sun. Mr. Paulenka, 55, started with the company 40 years ago as a bag boy, and is now its supervisor of facilities and operations.

He was one of several top managers who have been leading an unusual rebellion from within corporate headquarters against the new co-chief executive officers who work down the hallway as they all oversee the chain’s 71 stores and 25,000 employees. The company generates $4.6 billion in annual sales.

The feud within the Demoulas family, which runs the highly successful grocery chain in Massachusetts, New Hampshire and Maine, first spilled into public view — and into the courts — decades ago. The chain has its roots in a single market founded nearly 100 years ago by a Greek immigrant couple. By the 1950s, two of their sons were running the company, expanding it to 15 stores.

The two sons had been equal partners, but after one died, the other, little by little, took more control of the shares from his nieces and nephews. Eventually, the nieces and nephews sued their uncle for fraud, pushing all kinds of family business, including drug abuse and extramarital affairs, into the limelight. In 1994, a judge ruled in favor of the nieces and nephews and awarded them 51 percent of company stock.

But the other branch, led by Arthur T., a grandson, still controlled the board of directors until last year, when one member of the board switched alliances and gave control to his cousin and nemesis, Arthur S. Demoulas

The board accused Arthur T. of being insubordinate and spending money recklessly. Arthur T. was pushed out as president in June.

Nonetheless, Arthur T. was beloved by his employees, who announced on Thursday a “nonnegotiable demand” that “Artie T” — also known as “A.T.D.” and “Mr. D.” — be reinstated.

He and others disputed the board’s complaints, saying they were a cover for bad blood between the two branches of the family. The company has thrived on its strategy of offering good quality food at low prices, they noted. Their fear is that it will be sold, and it will have to raise prices, which could destroy its business model.

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“There comes a time in life when you have to make a stand for something that’s right,” said Joe Schmidt, holding the door.CreditKatherine Taylor for The New York Times

The company rebuffed the employees and on Thursday, in advance of Friday’s rally, issued a warning: “If you choose to abandon your job or refuse to perform your job requirements, you will leave us no choice but to permanently replace you.”

The new co-chief executives, Felicia Thornton and James F. Gooch, had no immediate comment after the rally. They have said they took the request to rehire Arthur T. to the board of directors, and were planning a conference call on Monday that would include representatives of the employees.

The labor action has caught the eye of analysts who say they have never seen anything quite like it.

“This is an unprecedented industrial action because it straddles both the management and the rank and file of this company,” said Christopher Mackin, a lecturer at Rutgers School of Management and Labor Relations, who came to observe the scene.

It has drawn notice, too, because of the gulf that workers often feel these days between themselves and management, like the so-called 1 percent that rules corporate America. Here, those in the 99 percent are standing up for a one-percenter, Arthur T. “He’s very personable and touched a lot of hearts in the community,” said Derrin Tassin, 24, a warehouse worker wearing a lip ring, earrings and a tank top that showed off his extensive tattoos. “He supported all of us, and it’s the least we can do to support him.”

Several other employees spoke of Arthur T.’s generosity and compassion. “He’s been to my kids’ weddings, my mother’s funeral, his sisters came to my mother’s funeral, to my brother-in-law’s funeral,” said Michael King, 57, the company’s controller.

Thomas Kochan, a professor of work and employment research at M.I.T.’s Sloan School of Management, said that such allegiance, as expressed through the top-to-bottom work action, was “very, very rare.”

“It’s this spontaneous, informal organization of people who have come together to protest the shift in management and strategy that’s so unusual,” he said. It happens in China, he said, but rarely in the United States.

Many employees said that they loved their jobs but were defiant toward the new management as they headed for the rally on Friday in the company parking lot.

“I’m not afraid to go look for another job,” said Nancy LeBlanc, 54, a front-end manager, as she walked across a field with her co-workers. “We want Arthur T. back,” she said. “He knows how to run the business. He stands by us, we stand by him.”

The rally was peaceful, and many store employees returned to work afterward, while many managers said they would not go back into headquarters.

It is not clear how the dispute may be resolved. But for some employees, a practical resolution was less important than standing up for a good boss who they believe was fired unfairly.

“There comes a time in life when you have to make a stand for something that’s right,” said Joe Schmidt, 42, supervisor of operations. “I’ll be able to tell my kids, I’ll be able to look them in the eye and say, ‘Daddy did the right thing.’ That’s important. It’s far more important than any job.”

A version of this article appears in print on , on Page A11 of the New York edition with the headline: Across a Grocery Chain, a Labor Protest in Support of a Manager. Order Reprints | Today’s Paper | Subscribe